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  1. Core Server
  2. SERVER-18966

Allow exclusion in $project stage of aggregation pipeline

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    • Minor Change
    • Query 11 (03/14/16), Query 12 (04/04/16), Query 13 (04/22/16), Query 14 (05/13/16), Query 15 (06/03/16), Query 16 (06/24/16)

      There is currently no way to easily specify that project stage keep all fields except for a particular one (with exception of _id).

      This can be helpful to limit the amount of data returned when some aggregation also needs to be done.

      Examples

      // Exclude a single field.
> db.example.insert([
  {_id: 0, a: 1}
]);
> db.example.aggregate([{$project: {a: 0}}])
{_id: 0}
> db.example.aggregate([{$project: {a: false}}])  // Means the same thing as above.
{_id: 0}

// Exclude a nested field.
> db.example.drop()
> db.example.insert([
  {_id: 0, a: {b: 1, c: 1}}
]);
> db.example.aggregate([{$project: {'a.b': 0}}])
{_id: 0, a: {c: 1}}
> db.example.aggregate([{$project: {a: {b: 0}}}])  // Means the same thing as above.
{_id: 0, a: {c: 1}}

// Exclude a nested field from an array.
> db.example.drop()
> db.example.insert([
  {_id: 0, a: [{b: 1, c: 1}, {b: 2, c: 2}]}
]);
> db.example.aggregate([{$project: {'a.b': 0}}])
{_id: 0, a: [{c: 1}, {c: 2}]}
> db.example.aggregate([{$project: {a: {b: 0}}}])  // Means the same thing as above.
{_id: 0, a: [{c: 1}, {c: 2}]}

            Assignee:
            charlie.swanson@mongodb.com Charlie Swanson
            Reporter:
            asya.kamsky@mongodb.com Asya Kamsky
            Votes:
            3 Vote for this issue
            Watchers:
            19 Start watching this issue

              Created:
              Updated:
              Resolved: